The invention relates to a method of manufacturing black tea. More particularly, a modification of the standard method of black tea manufacture that provides a significant improvement in liquor quality.
In the manufacture of black tea, young leaves usually 2-3 leaves and a bud are plucked and withered for about 12-24 hours to reduce moisture and to bring about desirable chemical/Biochemical changes. Withering process allows certain chemical and biochemical changes to occur and also the moisture content of the leaves is brought down from 90% to 50-70%. The tea leaves are then macerated using a Cut-tear-and curl machine (CTC machine) or rolled using rollers. This disrupts the cellular integrity of leaf tissues and allows oxidation of catechins by enzyme polyphenol oxidase which results in the development of colour pigments i.e. theaflavin and thearubigins. The macerated leaves are fermented for a suitable time and then fired at a high temperature to stop the enzyme activity.
The taste of black tea is a result of the complex interaction, between the polyphenols, caffeine, theaflavins and thearubigins that occurs during the fermentation. This interaction also contributes to the brightness, briskness, colour, thickness and body of black tea.
The price of tea depends on its quality and the quality of tea depends largely on the treatment steps. The quality of tea is evaluated based on parameters such as colour; brightness; tea flavour; body; bitter taste etc.
The applicants have found that the bitter taste of black tea can be significantly reduced by treating the plucked tea leaves with ammonium bicarbonate. This treatment also improves the brightness of tea, which is also a quality criterion.
United Kingdom patent specification GB 1,485,362 (Unilever) discloses treating black, green or oolong tea with an aqueous solution of ammonium bicarbonate or ammonia to improve the extraction of soluble solids. The compounds are suitable for use as a process aid as they leave negligible non-tea residue.
It is an object of the present invention to provide a modification of the standard method of black tea manufacture that provides a significant improvement in liquor quality.
The improvement in liquor is evidence in terms of brightness, yellowness, thickness and with astringency.
It is also an object of the present in invention to provide a modified method of black tea manufacture that provides black leaf tea from which infusions give a bright yellowish brown end cup that is superior to that prepared from standard processed black leaf tea.
The present invention relates to an improved process for the treatment of tea leaves consisting of the known steps for preparing black tea the improvement wherein comprises treating the tea leaves prior to the step of fermentation with ammonium bicarbonate having a concentration of 0.001 to 2% by weight of black tea for 10 minutes to 24 hours at a temperature between 10 and 45xc2x0 C.
The treatment with ammonium bicarbonate may be repeated at one or more stages prior to fermentation. Usually the known treatment for producing black tea commercially comprises the steps of withering followed by fermentation. The ammonium bicarbonate used for the treatment is food grade.
xe2x80x9cTeaxe2x80x9d for the purposes of the present invention means leaf material from Camellia sinensis var. sinensis or Camellia sinensis var. assamica. It also includes rooibos tea obtained from Aspalathus linearis however that is a poor source of endogenous fermenting enzymes. xe2x80x9cTeaxe2x80x9d is also intended to include the product of blending two or more of any of these teas.
xe2x80x9cLeaf teaxe2x80x9d for the purposes of this invention means a tea product that contains one or more tea origins in an uninfused form.
Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts or concentrations of material ought to be understood as modified by the word xe2x80x9caboutxe2x80x9d.